Control mechanism



July 20, 1954 c, E. oATEs x-:T AL 2,684,216

l CONTROL MECHANISM Filed Nov. 13, 195C 2 Sheets-smeet l ef 'www July 20 1954 c. E. oAT'E's. ETAL 2,684,216

CONTROL MECHANISM Filed Nov. 15, 195o 2 sheets-snee; 2

/Zlgi 2 55cm/azar 60A/moz wren-42 Patented July 20, 1954 CONTROL MECHANISM Charles E. Oates, Manhattan Beach, and Levi B.

Brookshire, Gardena, Northrop Aircraft, Inc., Hawthorne, Calif., a corporation of California Application November 13, 1950, Serial No. 195,282

Claims.

This invention relates to controlI mechanisms, and, more particularly, to an auxiliary mechanism for connecting two mechanical input circuits to one output circuit so that each input` or controll circuit directly operates the output circuit completely independently of the other input. The invention is especially suited for use in an aircraft surface control system where an auxiliary control system is to move a surface, such as a rudder, for example, in addition to the normal pilot-controlled movements. during iiight.

In high performance airplanes, stability of the primary attitude control. systems has become a major problem. At high wing loadings and high` altitudes, for example, it has been found necessary to improve the yaw damping characteristics. The basic method of achieving the improvement has been to automatically move 'the rudder surface in response to an airplane disturbance. This is in. addition to the normal automatic pilot, and should be accomplished so that the pilot is unaware of the automatic operation, except in noting the more desirable flying qualities of the airplane. It follows that the pilots controls must move the rudder without opposition from the servo system which provides the yaw damping, and that the yaw damping system must move the rudder, as required, without motion of the rudder pedals. Y

A push-pull link in the normal pilot-operated control system may be made extendable and put under the control of a positioning motor for automatically moving the rudder to obtain yaw damping. However, this link and its connection to the yaw damper actuator may have two or more joints which are subject to lost motion in the form of backlash, or free play.

Therefore, an object of the present invention is. to provide an intermediate mechanism for connecting in series two control input circuits to one control output circuit wherein no` backlash can occur in the connecting mechanism.

Other objects of this invention are to provide a connecting mechanism for the purposes described having highefciency and maximumrigidity (or minimum flexibility) so that a direct, positive control actioncan be maintained.

Additional objects and advantages willI be apparent from the detail description of a specific: apparatus embodying this invention, to follow.

Briefly, our invention comprises a cable and pulley systemv in which the. two` sides of the main cable control system pass. around an` idler pulley or pulleys rotatably mounted onf a stationary base., diverge outward'1y\and.then. each side. makes- Calif., assignors to an approximate o turn around a separate auxiliary pulley, and continues toward the end of the main control system approximately parallel to the opposite side cable. The two auxiliary pulleys are rotatably mounted on opposite ends of a bellcrank which is rotatable about a point equidistant from the auxiliary pulleys. Means are provided to rotate the bell'crank in accordance with movements of a secondary control system, which in this embodiment is a yaw damper actuator.

The invention will be more fully understood by reference to the accompanying drawings showing preferred' embodiments thereof, wherein:

Figure 1 is a perspective View of an airplane fuselage showing in diagrammatic form a rudder control system having a yaw damping system connected to move the, rudder with a mechanism of the present invention.

Figure 2 is a schematic plan View showing the intermediate control mechanism in the rudder system of Figure 1.

Figures 3 and 4 are schematic plan views, similar to Figure 2, showing slightly modified versions of the control mechanism.

Referring directly to Figure 1 for a detailed description of our invention, an airplane fuselage l mounts a rudder 24 controlled by movement of pilots rudder pedals 3 and l in the cockpit. When pushed forward, the right pedal 3 is connected in a conventional manner to pull a righthand rudder cable 5 forward along the right side of the fuselage I over guiding pulleys 5. Similarly, a left-hand rudder cable 'l is pulled' forward when the left pedal 4 is pushed forward,

andthe two` pedals are interconnected in opposite-moving manner through a torque beam 9. Since the rudder actuatingr unit to be described is power-operated, with noY feedback forces fromthe rudder surface, a two-way centering spring assembly i0 is connected to act between the fuselage structure Il and the pedals 3i and li to provide a neutralizing force.

Toward the aft end of the fuselage i, a cable drum I2 is mounted on a vertical drum axis |4 xed tothe struct-ure Il. Drum. grooves I5V are provided to carry the right-hand and left-hand,

cables 5- and l. Passing to the rear, each of these cables crosses' to the opposite side` and turns around separate idler pulleys. lrt, each. freely rotatable. on a. common axle Il. After this, the two cables 5 and 'i' cross again and extend outward'ly to, lead around: individua-l auxiliary pulleys I9 mounted on opposite. sides of aV bellcrank 2li. The, bellcrank 20. is locatedclosely behind the idler pulleys I6 and is rotatably carried on a vertical bellcrank pivot 2i. The auxiliary pulleys I9 are equidistant from the bellcrank pivot 2! and are positioned laterally opposite each other and slightly behind the pivot 2i when the controls are in neutral position.

The rudder cables 5 and l run rearwardly from the auxiliary pulleys I9 past rear guiding pulleys Sa and finally are attached on opposite sides of a control quadrant 22 rotatable about a fixed vertical quadrant axis 24. The quadrant 22 carries a rod connection 25 on one side thereof, to which a valve rod 2S of a hydraulic control valve 2 is connected. This valve 2 is secured on the side of a rudder actuating cylinder 25 containing` a forwardly extending piston rod 3S pivotally attached to the fuselage by means of the quadrant axis 24.

Within the actuating cylinder 2S, the piston rod Si@ carries the customary piston (not shown), and the closed end of the cylinder 29 is rotatably connected to a rudder control arm El which is fastened to a rudder hinge line fitting 32 for rotating the rudder 2 about a Vertical hinge line Edi. Flexible hydraulic supply and return lines f 35 connect to the control valve 2l for providing operating power to the cylinder 29.

The main rudder control system is thus described in general terms. When the bellcrank Ztl is stationary, it is seen that the rudder pedals 3 and i cause the right and left-hand cables 5 and l to operate around the auxiliary pulleys I9 just as around the normal guiding pulleys S and 5a to rotate the quadrant 22 and thus move the valve rod 2e into or out of the control valve 2l.

For rudder operation from a second control input, the bellcrank 2@ carries a lever arm S5 to the end of which is attached a yaw damper cable assembly 3i' extending at right angles to the lever arm 35. Two cable attachment points 3S on the arm 35 are provided, so that the damper cable 37 may rotate the bellcrank 2G without the backlash which could occur at the attachment, if only one were used, during reversals of direction.

The damper cable 3l leads around secondary pulleys Il@ to attach to an output sheave lll driven by a yaw damper actuator 42. This actuator 52 is energized by a yaw-controlling servo system, which forms no part of the present invention, however. The servo control system may comprise a rate gyro designed to develop an electrical signal Voltage proportional to the rate of yaw and/or side-slip of the airplane. This voltage then passes through a servo-amplifier to operate the electrical actuator 132.

To provide sufficient rudder movement to counteract the yawing tendencies, a maximum range of ten degrees rudder travel is usually required to be attained by the damper mechanism, thus allowing five degrees of rudder deflection on each side of a neutral damper position. rihe present invention accommodates this range very well.

Operation of the damper actuator i2 rotates the bellcrank 2@ about its bellcrank pivot 2l to displace the auxiliary pulleys I9 in opposite foreand-aft directions and thus cause actuation of the right and left-hand rudder cables 5 and l aft of the bellcrank 20. Forward of the bellcrank, the rudder cables 5 and 'l merely wrap or unwrap around the idler pulleys i5. rhis action takes place because of the very low force required to operate the valve rod 28 in this fullpower control system. The auxiliary mechanism is located as close as possible to the rudder actuating cylinder 2t to obtain short cable lengths,

4i minimum friction, and maximum rigidity. The rear guiding pulleys 6a, if necessary because of space limitations such as in the tail section of the fuselage l, are positioned so that each rudder cable extending rearwardly from the bellcrank 2@ makes substantially a 90 angle with the line joining the center of its respective auxiliary pulley it to the bellcrank pivot 2|, at the center rudder position, so that maximum rudder movement is obtained from a given damper actuator i2 movement.

The output of the yaw damper actuator i2 should be through an irreversible driving assembly lill before connecting with the output sheave si, so that normal rudder control by the rudder cables 5 and will not disturb the servo mechanism position, but will move only the rudder 2.

Referring again to Figure l, an auto-pilot servo unit 5 is shown cable-connected to the cable drum l2. This illustrates the preferred location of the autopilot driving mechanism in a control system using the present invention. The cables to this unit d5 thus move in synchronism with the main control cables 5 and l, and the rudder pedals 3 and li. That the drive pulley of the autopilot unit 45 is directly connected to rotate, by means of the unitary drum i2, when the rudder pedals S and i are operated. When the autopilot unit 45 is oirf it free wheels with the manual system, and vice versa, according to conventional practice. The small amount of friction in the autopilot cable and pulley system, when acting on the main control system at a point adjacent to the idler pulleys it, helps to prevent the tendency for the rudder control cables 5 and l forward of the bellcranl: 20 to move when the damper actuator l2 changes the valve rod 2S position. The centering spring assembly l! of course resists this forward cable movement tendency in response to damper actuator movement also.

If more restraint is desired forward of the idler pulley It?, a pivoted spring-loaded bar 4S may be installed so that a roller 4l carried at its unpivoted end is designed to engage a cut-out lill in the cable drum l2 when the rudder 2 is in neutral. Since the majority of the Flight trip time is made with the rudder neutral, the roller d? and cut-out 49 aid in isolating the yaw damping operation from the remainder of the main control cable system, so that better efficiency is attained by the damping system. This cable drum restraint, however, must not be strong enough to interfere with the pilots operations of the rudder pedals.

It is thus seen that a simple auxiliary, or secondary, control mechanism has been provided Iby the present invention. An important feature of this mechanism is that no backlash whatsoever can occur in the connection Gf the damping system to the rudder operating mechanism. The rudder control cables 5 and 'I are smoothly operated in yaw damping movements with no lost motion and a minimum of required power.

Several other forms of this invention will be readily apparent to persons skilled in the art. Figure 2 shows the same control mechanism geometry as in Figure 1. In Figure 3, for example, the bellcranlr pivot 2 I a is moved forward to a point on the circumference of the idler pulleys i6. In Figure 4, the bellcrank pivot 2| b is at the center of rotation of the idler pulleys i6. While the paths of motion of the respective points on the rudder cables 5 and 'l next to the forward side of the auxiliary pulleys I9, as the bellcrank 20 is rotated, do not exactly conform to involute curves of the circle represented by the idler pulleys I6, which would be the ideal condition, still this ideal condition is very closely approached for a small angular deflection of the bellcrank from its neutral position. For the relatively small angle (about 9 total) through which the bellcrank 20 is required to turn for yaw damping in the presently used system configuration, any of the illustrated geometrical forms are satisfactory` To obtain the most nearly equal amount of simultaneous cable Wrap and unwrap about the idler pulleys IS when the bellcrank 20 is rotated from a central position, the congurations of Figures 2 and 3 seem to be preferable. Another possible coniiguration, for example, is to employ two sets of idler pulleys rotatable about separate axes, instead of the idler pulleys i6 shown herein as being mounted on the common axle l1.

The important point to be understood is that the present invention is not limited to any one speciiic form, but it is possible to adopt other forms and modications. Also, other types of control systems may be substituted in place of the yaw damper device, such as a control surface trim system, for example. In fact, this invention is not limited to aircraft use only, but can be used in any control system where independent control of a single output is required from more than one input.

From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before enumerated as desirable, but which obviously is susceptible of modication in its form, proportions, detail construction and ar rangement of parts without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specic features shown, but that the means and construction herein disclosed comprise the preferred form v4of several modes of putting the invention into eiect, and the invention is, therefore, claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

What is claimed is:

1. In an airplane having a rudder connected for movement in ltwo directions by a two-cable rudder control system having means actuated by the pilot, a yaw damper control mechanism cornprising a yaw damper actuator, a bellcrank member rotatable on a fixed axis in said airplane, said actuator having a driving connection with said bcllcrank for rotating said bellcrank in either of two directions, two control pulleys rotatable on separate axes on said bellcrank on substantially opposite sides thereof and equidistant from said fixed axis, idler pulley means also rotatable in said airplane and located adjacent to said bellcrank, the two cables of said rudder control system passing from the pilot actuated means, around opposite respective sides of said idler pulley means, then diverging and passing, respectively, around said control pulleys to lead to said rudder, the point of contact of each of said cables on the side of its control pulley nearest said idler pulley means having a path of motion defined by an approximate involute curve about said idler pulley means when said bellcrank is rotated a relatively small amount,

whereby said yaw damper actuator can control said rudder automatically and independently of the pilot, wherein said idler pulley means is mounted on only a single idler axis in said airplane, said two rudder cables curving inwardly around opposite sides of said idler pulley means and crossing to extend to said control pulleys.

2. In an airplane having a rudder connected for movement in two directions by a two-cable rudder control system having means actuated by the pilot, a yaw damper control mechanism comprising a yaw damper actuator, a bellcrank member rotatable on a xed axis in said airplane, said actuator having a driving connection with said bellcrank for rotating said bellcrank in either of two directions, two control pulleys rotatable on separate axes on said bellcrank on substantially opposite sides thereof and equidistant from said fixed axis, idler pulley means also rotatable in said airplane and located adjacent to said bellcrank, the two cables of said rudder control system passing from the pilot actuated means around opposite respective sides of said idler pulley means, then diverging and passing, respectively, around said control pulleys to lead to said rudder, the point of contact of each of said cables on the side of its control pulley nearest said idler pulley means having a path of motion deiined by an approximate involute curve about said idler pulley means when said bellcrank is rotated a relatively small amount, whereby said yaw damper actuator can control said rudder automatically and independently of the pilot, wherein said driving connection does not permit rotation of said yaw damper actuator and said bellcrank when said rudder is moved by reciprocal motion of said rudder control cables, and including a follow-up member connected to move with said rudder control cables on the pilots side of said idler pulley means, a detent in said follow-up member, a lever arm pivoted on said airplane, elastic means connected to urge said lever arm against said follow-up member at all times, and a roller-shaped member projecting from said lever arm and positioned to engage with said detent at a neutral follow-up position, only, in a semi-latching condition, whereby reciprocal motion of said rudder cables from neutral is restrained when said bellcrank is rotated in either direction by said yaw damper actuator.

3. A mechanical linkage comprising a rst actuator, a device to be actuated, two oppositely moving taut cables connected to said rst actuator at one end and to said device at the other end, idler pulley means freely rotatable on only a single idler axis xed to a structural support, a bellcrank member rotatable on an axis which is parallel to said idler axis and xed to said support, said bellcrank having two substantially oppositely extending arms thereon, two auxiliary pulleys rotatably mounted one on each of said arms at points equidistant from said bellcrank axis, said cables leading from said rst actuator to opposite respective sides of said idler pulley means and passing partially therearound, then curving inwardly from opposite sides of said idler pulley means and crossing to extend respectively to the outer sides of said auxiliary pulleys, and passing partially therearound to lead to said device, the point of contact of each of said cables on the side of its auxiliary pulley nearest said idler pulley means having a path of motion dened by an approximate involute curve of the idler pulley means about which it is turned when said bellcrank is rotated a relatively small amount, a second actuator, and positive driving means connected between said second actuator and said bellcrank to rotate said bellcrank, said bellcrank axis being located adjacent to the circumference of said idler pulley means substantially at the crossing point of said cables.

4. A mechanical linkage comprising a iirst actuator, a device to be actuated, two oppositely moving taut cables connected to said rst actuator at one end and to said device at the other end, idler pulley means freely rotatable on only a single idler axis fixed to a structural support, a bellcrank member rotatable on an axis which is parallel to said idler axis and fixed to said support, said bellcrank having two substantially' oppositely extending arms thereon, two auxiliary pulleys rotatably mounted one on each of said arms at points equidistant from said bellcrank axis, said cables leading from said rst actuator to opposite respective sides of said idler pulley means and passing partially therearound, then curving inwardly from opposite sides of said idler pulley means and crossing to extend respectively to the outer sides of said auxiliary pulleys, and passing partially therearound to lead to said device, the point of contact of each of said cables,

on the side of its auxiliary pulley nearest saidil 5. A mechanical linkage comprising a rst actuator, a device to be actuated, two oppositely moving taut cables connected to said rst actuator at one end and to said device at the other end, idler pulley means freely rotatable on only a single idler axis iixed to a structural support, a bellcrank member rotatable on an axis which is parallel to said idler axis and fixed to said support, said bellcrank having two substantially oppositely extending arms thereon, two auxiliary pulleys rotatably mounted one on each of said arms at points equidistant from said bellcrank said cables leading from said first actuator to opposite respective sides of said idler pulley means and passing partially therearound, then curving inwardly from opposite sides of said idler pulley means and crossing to extend respectively to the outer sides of said auxiliary pulleys, and passing partially therearound to lead to said device, the point of contact of each of said cables on the side of its auxiliary pulley nearest said idler pulley means having a path of motion denned by an approximate involute curve of the idler pulley means about which it is turned when said bellcrank is rotated a relatively small amount, a second actuator, and positive driving means connected between said second actuator and said bellcrank to rotate said bellcrank, said bellcrank axis being located within the circumference of said idler pulley means substantially symmetrical with the cables extending from `said idler pulley means to said auxiliary pulleys.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 1,992,970 Sperry Mar. 5, 1935 2,182,648 ,Solomon Dec. 5, 1939 2,183,932 Carlson Dec. 19, 1939 2,542,946 Ross Feb. 20, 1951 vin- 

